Among various semiconductor elements, the amount of heat generated in a high power control power device used for controlling electric automobiles, electric vehicles and the like is large. Thus, for example, a power module substrate obtained by bonding a metal plate having excellent conductivity, as a circuit layer, to a ceramic substrate (insulating layer) composed of AlN (aluminum nitride) as a substrate on which the power device is mounted and bonding a metal plate having excellent thermal conductivity for radiating heat to the lower surface of the ceramic substrate as a circuit layer has been widely used in the related art.
In such a power module substrate, a semiconductor element is mounted on the circuit layer as a power device through a solder material.
In this kind of power module substrate, a metal part such as a radiator plate, a cooler, or a buffering plate is further bonded to the metal layer side in some cases.
For example, in PTL 1, a power module substrate is disclosed which has a circuit layer composed of Al formed on one surface (first surface) of an insulating layer and a metal layer composed of Al formed on the other surface (second surface) of the insulating layer. A power module substrate is also disclosed which has a heat sink (power module substrate with a metal part) obtained by bonding a heat sink (metal part) to the surface of the metal layer of the power module substrate by brazing.
In addition, in PLTs 2 and 3, a power module substrate is disclosed which has a buffering layer (power module substrate with a metal part) obtained by bonding a buffering layer (metal part) composed of aluminum to a surface of a metal layer of a power module substrate by brazing.
Further, in PTL 4, a power module substrate having a buffering layer (power module substrate with a metal part) obtained by bonding a buffering layer (metal part) composed of a metal matrix composite (aluminum matrix composite) to a surface of a metal layer of a power module substrate by brazing.
These power module substrates having a buffering layer are power module substrates with a heat sink obtained by further bonding a heat sink to the buffering layer.